Undercarriage for rotative wing aircraft



mzs, 1944. A CG PULLIN 2,339,871

UNDERCARRIAGE FOR ROTATIVE WING AIRCRAFT Filed April 6, 1940 3 Sheets-Sheet 1 Jan. 25, 19. c. G. PULLIN' UNDERCARRIAGE FOR ROTATIVE WING AIRCRAFT Filed April 6, 1940 3 Sheets-Sheet 2 Jan. 25, 1944. c. G. PULLIN UNDERCARRIAGE FOR ROTATIVE WING AIRCRAFT Filed April 6, 1940 3 Sheets-Sheet 3 2.339.877 msacsreemcn ro'n ROTATIVE wmc AIRCRAFT Cyril George Pullin, Genista, Newton Mearns, Scotland, asslgnor to Autogiro Company of 7 America, Willow Grove, Pa... a corporation of Delaware Application April 6, 1940, Serial No. 328,234 In Great Britain April 11, 1939 4 Claims. (Cl. 244 104) The present invention relates to rotative wing aircraft and is applicable to aircraft having one or more rotors disposed on a vertical axis above the fuselage of the aircraft but is also applicable to aircraft having two or more rotors mounted and provided with a main undercarriage vwith castering wheels and asteerable tail wheel. It is to be understood that this embodiment is illustrated by way of example only and that the preson opposite sides of the longitudinal axis of the aircraft. I

It-has been found 'in the course of practical tests with rotative wing aircraft, and more especially with helicopters. that the ground interference or echo effect caused by the slipstream of the rotor (or rotors) produces considerable instability of the aircraft when it becomes just airborne. In the case of an aircraft having two rotors disposed one on each side of the fuselage there is available a certain amount of lateral control produced, for instance, by differential pitch change of the two rotors which gives the necessary stability about the longitudinal axis. In the case of a machine having a single rotor or two coaxial rotors arranged one above the other it is not possible to effect lateral correction of the aircraft without such correction being accompanied by lateral swing of the machine. with the aircraft say a few inches off the ground when the wind direction suddenly changes, the corrective'moment will cause a lateral swing and at the same time the aircraft will tilt until one of the wheels touches the ground. With an undercarriage of normal construction in which the wheels areflxed in a fore and aft direction, this will produce an overturning moment on the aircraft which cannot be corrected by the rotor control and which may cause the aircraft to turn over. The effect is somewhat similar to that produced by side-slipping of the aircraft since there is lateral movement of the aircraft relatively to the ground.

According to the present invention a rotative wing aircraft is provided with landing wheels which are capable of castering freely as required by the velocity of the aircraft relatively to the ground. The aircraft may be provided with any desired formof undercarriage, the main wheels of which are capable of castering freely while the subsidiary nose or. tail wheels may either be f arranged 'to caster or be fixed in position as desired. v A feature of this invention consists in providing means for steering one or more of the groundcontacting" wheels .of the aircraft to facilitate taxiing, V v i The accompanying drawings illustrate an embodiment of this invention as applied to a rotative wing aircraft having a single sustaining rotor c of this particular construction.

ent invention is not limited in scope to aircraft In the drawings:

Fig. 1 is a diagrammatic front elevatlonal view showing a rotative wing aircraft in a side-slipping attitude;

Fig. 2 is a view similar to Fig. 1 showing the aircraft just after one of the main undercarriag wheels has contacted the ground;

Fig. 3 is an enlarged sectional view through one of the main undercarriage struts;

Fig. 4 is a front elevational view of the strut illustrated in Fig. 3 showing it in the extended position;

Fig. 5 is a view similar to Fig. 4 showing the strut compressed;

Fig. 6 is a sectional view on the axis of the steerable tail wheel; and

has a tail wheel l6 carried by a shock absorbing strut ll which is steerable as will hereafter be described with reference to Fig. 6.

Referring to Figs. 3, 4; and 5. These figures show the construction of the main undercarriage comprising the shock absorbing struts l4 and wheels IS. The wheel l5 has an axle 20 by which it is secured to forks 2! which join at'their upper end and are extended upward by a cylindricalzpart 22'which is continued by arod 23 which runs up through the centre of the strut l4. Surrounding the cylindrical part 22 is a roller bearing 24 which supports said cylindrical part within a recess 25 .at the lower end of a plunger 26 which is vertically slidable within the strut M. The upper end of the rod 23 has secured toit a pin zl-which coacts with a ring 28' secured by an internal screwthread 29 within the strut l4 and having an aperture 30 through which the rod 23 is freely slidable. A compression coil spring 3| is disposed between the lower face of the ring 28 and the upper face of the plunger 26 so that it surrounds the rod 23 and is enclosed within the strut M. This spring 3| protides-the shock absorbing action of the undercarriage but it is to be understood that the simple spring arrangement herein described may be replaced by any desired form of'shock absorber, for instance of an hydraulic type.

The roller bearing 24 between the cylindrical part 22 carrying the wheel I5 and the' plunger 25 allows relative turning between them to permit of free castering according to the direction of rotative motion between the aircraft and the ground at the moment of contact. j

Asshown in Fig. 4 the pin 21 at the upper end of the 'rod 23 cooperates with a V-shaped notch 32 on the upper surface of the ring 28 so that when the spring 3| is fully extended the rod 23 is maintained in a position such that l the plane of the wheel I5 is approximately in a fore and aft direction of the aircraft, thus reducing'wind resistance. A similar pin 33 is carried by an annulus 34 keyed at 35 to the cylindrical part 22 and cooperates with a V'- craft side-slipping and it will be observed that the wheels l5, l5 are'both disposed in a fore and aft direction and that the tail wheel I8 is also in a similar position. Fig. 2 shows the aircraft immediately after the wheel I5 of the main undercarriage has touched the ground; It will be noted that the shock absorbing strut I4 is partly compressed and that the wheel I5 is castered to a position in which it allows the aircraft to shaped notch' 36 at the lower end of the strut I I4 to maintain the plane of the wheel l5 in a fore and aft direction when the shock absorbingstrut is fully compressed by the weight of move freely in a lateral direction, thus avoiding the setting up of an overturning moment. when the other wheel I5 comes into contact with the ground it will also ca'ster to a similar position.

It is not essential that the tail wheel. I 6 should be'allowed to caster as normally this wheel will touch the ground after the wheels l5, l5 of the main undercarriage, though if desired castering action of the tail wheel mayalso be provided for.

What I claim is:

1. In a rotative wing aircraft a main undercarriage comprising a pair of wheels, forked members carrying each of the wheels and tumthe aircraft, as indicated in Fig. 5. Thisallows the aircraft to resist cross winds when station- .ary on the groimd or while it isbeingtaxied,

but does not-in any way reduce-the ability of the wheel l5 to caster since it takes an appreby the weight of the aircraft and moreover the able relatively to fixed parts of the undercarriage to permit castering action of the wheels, shock absorbing means operative between the forked members. and the fixed parts of the undercarriage, pins carried by the forked members, said 7 fixed parts of the undercarriage having notches ciable-time for the spring 3! to be compressed offset of the axle 20 from the castering axis is suihcient ,to prevent premature engagement of the pin a: inthe notch as. 7 Such engagement is Figs; 6 and'l'show the construction of the steerable tail wheel. The wheel I6 is carried by an axle 40 which extends between the pair of vertical forlas'i carried by a cross member 42 integral witha cylindrical part 43 extended upwardly through the centre of the strut II by a rod 44. Surrounding the cylindrical part l3 is a roller-bearing 45 which'is disposed between said cylindrical part '43 and a plunger 46 which is vertically slidable in the strut ll. Secured within the strut I1 is a ring 41 having an'apere ture 48 through which the rod .44 is 'freely slidbale in an upward direction, downward move- Iment being restrained by a collar 49 mounted on the rod 44. Disposed between the lower sur: face of the ring" and the upper surface of the plunger 45 is a compression coil spring 50 which resists upward movement of the tail wheel IS.

The upper end of the rod is splined-as indicated at 51 and passes through a locating 52 at the upper end of the strut I]. The splines 5| carry a pinion 53 maintained'against vertical'movement by means, (not shown) meshing with a second pinion 54 keyed at 55 to a shaft 55 by which the tail wheel is steered. It is to be understood that the shaft 55 is coupled to a pilotssteering control, such for example as a rudder bar. Extending upwardly from the upper end of the rod. 44 is a pin 5'l coupled by a mechanical linkage or otherwise to the rotor strut'i'I-is compressed the pitchyof the rotor is decreased thereby reducing the lift. The pin 51 therefore preventeduntil the lateralspeed ofg the aircraft is reduced to an innocuous value.

adapted to engage and hold said pins when the shock absorbing means are fully extended or fully compressed to locate the wheels in generallyfore and aft direction, said pins and notches being out of engagement when the shock absorbing means are partially compressed.

2. In a'rotative wing aircraft, a main undercarriage comprising a pair of landing wheels each having a shock absorbing strut, a member in which the wheel is mounted, said member being carried by the strutand being turnable with respect thereto to permit castering action of the wheel, shock absorbing means operative between said member and said strut, and centering means having parts which come into engagement to center the wheel in a vertical plane generally fore and aft of the aircraft when the respect thereto to permit castering action of the wheel, shock absorbing means operative between said member and said strut, and centering.

means having parts which come into engagement to center the wheel in a vertical plane generally fore and aft of the aircraft when the'air- A craft is in flight or when the shock absorbing means is fully compressed under the weight of the aircraft, said parts being out of engagement to permit castering when the shoclr'absorbing means is partially compressed.

- pitch control and so arranged that when the may also be arranged to apply a rotor brake under these conditions.

The operation ofthe main undercarriage is best seen in Figs. 1 and 2. Fig- 1 showsthe air- 4. In a rotative wing aircraft, a shock absorb ing strut, a landing wheel and a member' in which said wheel is mounted, said member being carried by the strutand being turnable with respect thereto to permit castering action of the wheel, shock absorbing means operative between said member and said strut, centering means to center the wheel in a'vertical plane I generally fore and aft of the air'crait, said cenmeans comprising pins carried by said terlng member, and cooperating v-shaped notches in said strut, said notches being so located that the sides thereof "will engage the pins to move and held the pins in such position that the wheels are centered in said plane when the pins engage the notches, the pins engaging the notches only when the shock absorbing means is fully compressed under the weight of the aircraft or when the aircraft is in flight, said pins being disen- 5 gaged from the notches when the shock absorb-' in: means is partially compressed.

Y CYRIL GEORGE PULL-1N. 

